Force oscillation and phase transition of simple fluids under confinement

Area of Science:

• Physics
• Materials Science
• Computational Chemistry

Background:

• Understanding fluid behavior under confinement is crucial for tribology and nanotechnology.
• Surface force measurements often exhibit oscillatory behavior, but the underlying mechanisms require detailed investigation.

Purpose of the Study:

• To elucidate the force oscillation mechanism of a simple fluid confined between two surfaces using molecular dynamics simulations.
• To investigate the nature of the layering transition and the resulting solid phase structure.

Main Methods:

• Molecular dynamics (MD) simulations were employed to model a simple fluid confined between two surfaces.
• Force profiles were calculated and analyzed to understand the interaction dynamics.

Main Results:

• Simulated force profiles qualitatively matched experimental surface force measurements.
• The layering transition was identified as an abrupt liquid-to-solid phase transition.
• A hexagonal close-packed (hcp) crystalline structure formed in the confined solid film, exhibiting asymmetric mechanical properties.

Conclusions:

• The study confirms the abrupt nature of the liquid-to-solid phase transition under confinement.
• The asymmetric mechanical properties of the hcp structure influence oscillatory forces during normal approach and retraction.
• MD simulations provide a valuable tool for understanding complex interfacial phenomena in confined fluids.